So, I suppose that women who might be overweight or those with a disability, lower back pain, should not have kids then because being able to get up a slide is what counts as a parent. I would think that maturity, self-confidence, experience, knowlege, etc, all those things gained by 40 would count. I know I would rather a confident, self-secure, intelligent and wise woman, over a 20 to 30 year old who might go up the slide but is constantly insecure, still trying to figure out the world and how to be a woman and an adult. Someone who is gaining their learners permit on me.
I know this might come as a shock to you, but 40 is not ancient, your body doesn't disintegrate when you turn 40 or 50. I have seen 70 and 90 year olds doing things that I would find difficult, like digging the back yard to build a garden. It doesn't matter what age you are, you can still be fit and strong.
Besides, children should be spending most of their time with other children. I have now raised two of my own, they only wanted to know me for as long as it took to get them to kindi and later school. Once they hit five, you are only cramping their style if you try and hang out with them. lol.